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led question

Discussion in 'Electronic Basics' started by Klemen, Jul 1, 2003.

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  1. Klemen

    Klemen Guest

    Hi!

    I'd like to connect 5 leds, but i'm not sure which way is better. Is it ok
    to connect them in series with a restitor to limit the current, or should i
    connect them parallel each with the resistor?

    regards
    Klemen
     
  2. Either of those may work, but connecting several in series may make
    more efficient use of the supply voltage, if it is quite a bit higher
    than the LED requirements. What supply voltage are you using, and
    what color of LED?
     
  3. Klemen

    Klemen Guest

    I'm using 12V(actually 14V because it's a car battery) power suply and
    bright blue leds.

    thanks for your replies
     
  4. Since getting the utmost efficiency is not so important (unless you
    are going to leave them on for days without running the car) I would
    connect them in series in pairs , with a resistor for each pair.
    Since car battery voltage can spike around and vary quite a bit, I
    would go for about 10 ma (.01 amp) average. Blue LEDs drop about 3.5
    volts, each, so a pair will use up about 7 volts. That leaves about 7
    volts to be dropped by each resistor while carrying about .01 amp.
    7/.01=700 ohms, which is not a standard 5% value. 680 or 750 ohms
    would work fine. The heat produced in each resistor is about
    ..01*.01*700=.07 watts, so 1/4 watt resistors are plenty big.
     
  5. Tradius

    Tradius Guest

    Hi!

    The way you connect 5 leds doesn't make a difference in terms of theory.
    You can build parrarel or series cicuit. Either way is good because in both
    connections current flowing through leds must be the same and the voltages
    dropped on them also. So, the only difference betwen both types of
    connection
    is the voltage applied and the number of resistors. You should decide which
    is better: use more resistors and less voltage or vice versa.

    Tradius:)
     
  6. Klemen

    Klemen Guest

    Thank you everyone for your help!

    regards
    Klemen
     
  7. roma

    roma Guest

    So when one goes bad they all go out .
    roma
     
  8. If it goes bad by going open circuit, then that string will go out.
    If it goes bad by going short circuit, the rest of the string gets
    brighter. If the LEDs are operated well within their ratings (say
    half of maximum current rating) either case is very unlikely in your
    lifetime.
     
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